1. Field of the Invention
This invention relates to a casting die comprising a mold half with a mold insert disposed at least partly in a relief of the mold half.
2. The Prior Art
Casting dies usually have two mold halves, wherein individual mold halves may be constructed from several individual parts. In order to be able to make different castings with one casting die, it is customary not to form the negative contour: of the casting to be cast directly in the mold half, but instead to insert, within a relief of the mold half, several mold inserts that form the negative contour of the casting to be cast.
For this purpose, the mold inserts are inserted in a perfectly fitting relationship into the relief of the mold half and fastened immovably thereto with screw connections. Because of the perfectly fitting configuration of the mold insert and of the relief of the mold half, it is not possible for the mold insert to execute a lateral movement relative to the mold half. By fastening the mold insert with a screw connection, a vertical movement of the mold inserts relative to the mold half is additionally ruled out.
For a casting process, the mold halves are brought together, whereby one mold insert is usually pressed against a complementary mold insert in the second mold half, and a cavity, which will be filled with molten material during the casting process, is formed in their interiors. After filling of cavity with molten material and a solidification of the molten material, the mold halves are again moved apart and the solidified casting is removed from the mold inserts.
This separation process has the consequence that the mold halves can cool at different rates and thus a temperature difference develops between the mold halves. This temperature difference means that the mold inserts can also cool at different rates, shrink and exhibit a deviation of their position relative to their starting position.
The different cooling rates of the mold halves can accordingly lead to off-centering of the mold halves relative to one another and especially of the mold inserts disposed in the mold halves. Such an off-centering has the consequence that, in a subsequent casting process, the mold inserts do not bear ideally on one another but instead exhibit an offset relative to one another and that consequently unwanted defects can occur in the casting, especially different wall thicknesses.
In simple molds, which are provided with only one mold cavity for production of one casting per molding process, such an off-centering may possibly be compensated for by a manual realignment of the mold halves. The situation is more problematic for so-called multiple molds. These are provided with several mold cavities within the casting die and therefore have the ability to create several castings with the same casting die during a casting process.
A temperature difference between the mold halves and also between individual mold cavities of the casting die can also occur in such casting dies. However, this has the consequence not that the mold inserts, which form or encompass the mold cavities, are off-centered in identical manner, but instead that individual mold cavities or the mold inserts exhibit different off-centering from their complementary mold inserts.
Until now it has not been possible to eliminate such off-centerings in a simple manner, which has the consequence that more intensive post-machining is required for finishing of the casting. Precisely for rotationally symmetric castings, which during their intended use execute a rotary motion, it is important that the casting be uniformly machined in order to permit a movement that is as smooth-running as possible.
At present, such castings must be balanced in a complicated manner after the casting. However, the balancing can compensate for casting defects, especially different wall thicknesses to only a certain degree. In order to produce as few rejects as possible, it is accordingly important to avoid or at least minimize casting defects, especially different wall thicknesses of the casting.